Alcohol, used by the mother during pregnancy, can compromise fetal development. Drinking in the last trimester of pregnancy, when the brain growth spurt occurs, has been implicated in altered neuro-psychological functioning. Brain growth is also rapid in the period after delivery. If alcohol is used by the mother during lactation, the rapidly growing brain can again be exposed to small quantities of ethanol via mother's milk. Only one study of human infants has explored this question; the result was that infants exposed to as little as one drink a day, on the average, exhibited decrements in motor development. Although troubling, a single study is insufficient to establish the association. Here we propose an investigation to confirm or reject the hypothesis that drinking during lactation is associated with alterations in infant cognitive, motor, or somatic growth. The proposed study is nested within an ongoing longitudinal prospective study of 15000 pregnancies. Women complete questionnaires during pregnancy and at frequent intervals after delivery. there are 2 parts to this research: (I) Statistical analysis of all 15000 pregnancies to ascertain alcohol exposure of the infant via breast milk, and assess whether there are independent associations with outcome up to 18 months of age (growth, behavior, temperament, motor and mental development). These outcomes being relatively crude, a finer- scale study (II) is also proposed. Thus, from the present study, women who breast fee for 3 months, giving no supplemental formula, will be identified. From them, 3 groups will be selected according to postpartum alcohol exposure (non; 1/week but <1/day; at least 1/day). The 3 groups will be matched on smoking and drinking during pregnancy. In parallel, 3 groups of mothers who never breast fed will be chosen using the same alcohol exposure criteria. The infants will be examined at 3 years of age. Infant developmental scores and growth parameters will be related to exposure to alcohol via breast milk, using regression analysis to control for any confounding variables.